Signaling system



June 10, 1930.- A F, BENNETTETAL 1,762,139 I SIGNALING SYSTEM Filed Nov. 19. 1926 Arf/u/r f Ben/762% Patented June 10, 1930 vMTED-T A ES ARTHUR r. BENNETT, or ,RIcH MoNn HILL, ANn-cmr'ronn E. TMITCHELLMOF NEW YORK, N. Y., AssIG ORs a-BELL TELEPHONEVLABOB-ATORIES, rNconronATnn, I V Y or NEW YORK,'-I\T. -Y., A CORPORATION or ew YORK I r, a

' SIG ALIN sYsTn'm Application'filed November 19, 192 Serial N5." 149,301.

' This invention" relates to signaling systems,

particularly those employingcarbon button equipment in machine switching systems, set,

transmitters.

An object of the invent-ion is to protect instruments' in the circuit from the harmful effects of high frequency oscillations such as are set up by switching operations.

A further obj ectof the invention is to preventelectrical packing or cohering of the carbon granules of a transmitter.

It has been found that 'n atelephone system, switching operations, such as the operation of the switchhook to signal the operator, the operation of the calling dial when the transmitter short-circuiting contact fails toQ of hwherinductanee but ofinherently higher function, or the operation of the central ofiice up high frequency oscillations of comparatively high voltage which cause electrical packing or cohering of the carbon granules in the transmitter. This cohering persists until relieved by a mechanical disturbance or otherwise and reduces the resistance of the transmitter and decreases it s sensitivity. The most troublesome effects frequently experienced are produced by the operation of the switchhook, so that in the ordinary types of desk and wall phones inwhich the mechanical shock accompanyingthe operation of the switchhook at least partly'restores the transmitter toits normal condition, there areno particularly deleterious consequences, although the packing may'shorten thelife of the transmitter. However, the transmitter of a handset is not mechanically disturbed bythe operation of the cradle switch and the packing resultingfromsuch operations produces an objectionable reduction in efiiciency,

' In accordancewith this invention there is connected between the transmitter and the circuit into which it operates, a circuit. or A operatoror whenthedialing'swit'ch}5 is operated,high frequency oscillationslar e set up in the circuit dueto the effect .ofthje inducseries inductance andshunt capacity. However, a condenser of proper value connected jwill be so large as to give'the shunt path a' high impedance. Also the series inductance elements must have very low distributed capacity. For this reason a 3oi10f-1ow jinductanceand minimum distributed capacity found that similar protection is often desirembodiment thereof 'ina telephone subseti' in shunt to the transmittergreatlyreduces the e'fiectof the disturbances. Y

- v Since thetroublesome oscillations are of a very high frequency,those of chief impor I tance being of the order of'several hundred thousand cycles per second or higher, it is "necessary that the leads associated with the shunt condenser be very short otherwise their inductive reactance at these high frequencies may be found moreadvantageous thana coil distributed capacity.

to 'the protection of transmitters it" has been able for other light contact'devi'ces. j Forex ample, similar arrangements have been found advantageous for protecting voicefrequency. relays, t

e light contacts of which may other W156 where or freeze d'u'e'to' the high voltages of the oscillations set up by switching operations, or other disturbances either-originals derstood reference to the following de ta led description [in connection With the ing in the circuititself or p roduc'edby an'out- 1 "side source of energy- Thisinvention be more readily 'unto drawing which shows diagrammaticallyio'ne There is shown a subscribersset comprismg atransmitter 1, a rece1ver-2, calling hell 3,

switchhook or cradle switch 6 connected. in

When the switch Giso'perated tosignalthe tance coil 4 and the capacity of the'windin gs and connections. These oscillations are of comparatively high voltage and, cause 'the granules of the transmitter'to pack,re'ducing the resistance'and eificiencyof the instrument. In theordinary wall or desk setin which the inductance coil-4;, dialingswitch 5, and a inductance coils alone.

switch 6 and transmitter 1 are mounted together, the operation of the switch jars the transmitter and loosens the carbon granules. However, in a hand set in which the switch 6 is operated, while the transmitter and receiver are held in the hand, there is very little or no restoring effect.

In order to protect the transmitter from these oscillations, inductance coils 10 and 11 are connected in-series in the connections lead ing to the transmitter, and a condenser 12 is connected in shunt to the coils and transmitter. These elements form a low pass filter which transmits the voice frequency currents generated by the transmitter but effectively suppresses the high frequencyoscillations produced by the switching operations. The effect of the inductance coils is further increased by winding them on the same coil in series aiding relation. Since the troublesome oscillations are of very high frequency, the most important being of the order of several hundred thousand cycles per second, it is necessary that the connections 13 associated with the condenser 12 be very short. Otherwise, their inductive reactance at these high frequencies will be so large as to give a high impedance in the shunt path thus in efi'ect counteracting the action of the condenser. For a similar reason, the coils 10 and 11 must be designed to have very low distributed capacity.

In one embodiment it was found satisfactory to give the condenser 12 a value of 0.006 microfarads and each of the coils 10 and 11 a value of self inductance of 0.00014 henries.

In some cases sufficient protection may be obtained by the use of the condenser or the However, most effective protection is obtained by the u'se'of both elements.

What is claimed is; 1. In a telephone substation circuit, a carbon button transmitter, and means for preventing switching operations from causing electrical packing in the transmitter, said means comprising an inductance element in series with the transmitter and a capacity element in shunt to the transmitter and inductance element.-

2. In atelephone subscriber set, a carbon button transmitter, an inductance coil in se- I ries with each terminal thereof, and acondenser in shunt to said transmitter and inductance coils,said condenser, coils and the associated leads having such impedance values as to preventultra audible transient oscillations, such as are set up by switching operations, from causing electrical packing in the transmitter.

3. In combination, a circuit containing a carbon button transmitter, a switching device, and means comprising a condenser connected between said switching device and said transconnected in shunt to said transmiter for preventing packing of the carbon in said transmitter.

In witness whereof, we hereunto subscribe our names this 17th day of November, A. D.

ARTHUR F. BENNETT. CLIFFORD E. MITCHELL. 

